Okay, so. Bearing in mind that I'm pretty drunk? The short answer - about all I'm capable of at the moment - is that it became clear early on that it was easier and more practical to simply create either a fully-tracked vehicle, or to enlarge the wheels on a vehicle that you'd usually expect to see moderately rough terrain like a truck or weapons carrier.
In reality, the half-track came about as something of a stopgap solution to a problem that didn't really exist in the first place; developments in tyres and vulcanization would mean that you could get better and bigger tyres that were capable of inflating and deflating to a degree that meant they were able to traverse muddier terrain without having to worry about the complex track arrangements you'd see on a half-track.
Really, it's far easier to have a driver trained to change a tyre than it is to worry about whether or not your crew of fucknuts can whip off a track and change a suspension assembly under fire. Half-tracks came and went super quickly in the span of modern warfare simply owing to the fact that there were a dozen ways to do what a half-track offered even better, more simply, and with a fraction of the materials.